Newbie question- how initialize some variable at adress. \ VOGONS

Newbie question- how initialize some variable at adress.

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First post, by deimond

Posted on 2012-12-05, 22:33

deimond Offline

Rank Newbie

Rank: Newbie
Posts: 9
Joined: 2012-11-29, 22:32

hi,

I'm a newbie in c and dosbox.
What i want to do is to initialize on adress lets say 0x2b0 a 1 byte value 0x00. How and where i can do that in the simplest way?
What i want is the program who read a byte from adress 0x2b0 get the static value defined in code.

Reply 1 of 1, by ripa

Posted on 2012-12-06, 15:49

ripa Offline

Rank Oldbie

Rank: Oldbie
Posts: 559
Joined: 2005-04-18, 00:53
Location: Finland

1char* address = 0xA0000;
2*address = 0x55; // write 0x55 to 0xA0000
3printf("contents of %p is %x\n", address, *address); // read from 0xA0000

You can verify this with Valgrind (since the address I used was unallocated):

1==10002== Invalid write of size 1
2==10002==    at 0x400589: main (in /secret/path)
3==10002==  Address 0xa0000 is not stack'd, malloc'd or (recently) free'd

edit: Added reading example.

edit2: Better answers here. You might need to use "volatile".

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